Investigation of Surface Alkylation Strategy in SOMC: In Situ Generation of a Silica-Supported Tungsten Methyl Catalyst for Cyclooctane Metathesis

Abstract

An efficient and potentially scalable method is described for the synthesis of the silica-supported complexes [(≡Si–O−)WMe5] and [(≡Si–O−)WMe2(≡CH)] obtained by in situ alkylation of the surface-grafted tungsten chloride [(≡Si–O−)WCl5] (1). [(≡Si–O−)WCl5] can be readily prepared by the reaction of commercially available and stable tungsten hexachloride WCl6 with partially dehydroxylated silica at 700 °C (SiO2-700). Further reaction with ZnMe2 at room temperature rapidly forms a mixture of surface-alkylated tungsten complexes. They were fully characterized by microanalysis, FTIR, mass balance, and solid-state NMR (1H, 13C, 1H–13C HETCOR, 1H–1H double quantum and triple quantum) and identified as [(≡Si–O−)WMe5] and another product, [(≡Si–O−)WMe2(≡CH)]. The latter might have been generated by partial decomposition of the tungsten methyl chloride compound, which is formed during the stepwise alkylation of [(≡Si–O−)WCl5]. DFT calculations were carried out to check the relative stability of the tungsten methyl ...